The invention relates to a method and apparatus for quantity controlled, continuous liquid exchange in distillation plant and absorption refrigeration circuits in which on the one hand a liquid mass feed, to be controlledly supplied into the high pressure zone, of enriched starting solution is raised from a low pressure level to a high pressure level and on the other hand the liquid flows, which are separate from each other, are in sum the same in quantity and are to be withdrawn from the high pressure zone, of the product condensate and of the depleted solution are brought from a high pressure level to a low pressure level.
In such a mass separation plant continuous operation is only possible if on there is both a continuous feed of defined liquid mass flow of enriched starting solution into the separating apparatus and two liquid flows, which are equal in sum, that is to say the depleted solution and the product condensate, are continuously removed from the apparatus in equal quantity. It frequently occurs that this mass separation takes place at high saturation pressures, as for example in the case of the separation of ammonia and water in absorption refrigeration circuits for the generation of heat for heating purposes at saturation pressures between 20 and 30 bar, while the starting solution is available with a pressure between 1 and 5 bar.
In such cases mechanical energy is used to increase the pressure of the starting feed solution from a low pressure level to the high pressure level of mass separation and the liquid flows, which are to be discharged. These liquid flows are transferred in the reverse manner with the dissipation of a large amount of mechanical energy from the high pressure level of mass separation to the low pressure level of the enriched starting feed solution.
In order to perform such liquid exchange in a present-day separating plant, it is necessary to have a high pressure pump for feed of the enriched starting solution into the apparatus and a respective chock valve for the reduction in pressure of the liquid flows which are to be removed in equal quantity.
While an industrial high pressure distillation plant is in the majority of cases run at a defined load point and thus may operate with adjusted exchange mass flows, in the case of absorption heat pumps the mass separation rates and accordingly the quantities of liquid to be exchanged have to be continuously varied to suit changing requirements. The expenditure on automatic control systems is substantial and involves a large proportion the total costs. In the case of absorption heat pumps with a small producer rate there is the further difficulty that a defined exchange of relatively small amounts of liquid is necessary across relatively high pressure differentials, for which there are however no miniaturized, efficient pumps and choke means whose mass flow may be automatically controlled. Such components must have a robust, hermetically sealed design and must be able to be produced without excessive complexity and expense of manufacture.
Development has so far been centered on the design of such components on the basis of pumps with a reduced drive energy requirement, especially positive-displacement pumps of the most varied types such as gear pumps, diaphragm piston pumps or axial piston pumps.
The German Pat. No. 3,133,387 for example describes a positive displacement axial piston pump for the feed of solution in connection with low power absorption heat pumps, which is driven with refrigerant vapor produced in the high pressure zone. Although this pump is robust in design and may be operated continuously with a piston stroke rate in line with needs, there is the significant disadvantage that the pump is not able to utilize the mechanical energy released during the solution exchange as driving energy and thus the drive energy requirement of the pump is only reduced by an amount equal to the losses of the electric drive. Furthermore, the liquid flows to be removed, that is to say the depleted solution and the product condensate, still have to be adapted to the requirements, this involving an extensive automatic control system.
The German unexamined specification No. 3,227,030 describes a solution exchange apparatus in the form of an axial positive displacement machine, in the case of which the mechanical energy of the depleted solution to be removed from the apparatus is to be transferred to the enriched starting feed solution in order to reduce the energy requirement for the supply of the solution into the apparatus.
This solution exchange means does however suffer from the disadvantage that it is only capable of intermittent operation and that in it the depleted solution has a tendency to spontaneously form vapor bubbles in the displacement chamber, this interfering with the quantity regulated solution exchange and decreasing the working life of the apparatus. Furthermore, the hermetically sealed electromagnetic drive hardly leads to an economy in energy and is not sufficiently powerful to feed the larger mass flow of the starting solution into the high pressure zone taking into account internal losses of the apparatus and the additional pipe pressure losses. The apparatus furthermore fails to utilize the mechanical energy fraction of the refrigerant condensate which is to be continuously removed from the apparatus and to be depressurized so that for the controlled feed of the refrigerant into the refrigerant evaporator it is still necessary to have a controlled high pressure reducing valve.